Professional oxide manufacturers use ethanol solution impregnation method to prepare Cu/MgO-Al 2 O 3 catalyst with highly dispersed metal Cu. On the premise of ensuring similar dispersion of Cu, the influence of the ratio of alkali center to metal center on the hydrogenolysis activity of glycerol was investigated by adjusting Cu loading and Mg/Al ratio in MgO-Al _ 2 O _ 3 composite oxide carrier respectively, in order to reveal the essence of the promotion of the carrier surface alkalinity on the hydrogenolysis reaction rate of glycerol.

In order to prepare Cu catalysts with similar dispersion and better compare the influence of alkalinity of oxide carrier on hydrogenolysis activity of glycerol, we need to obtain MgO-Al 2 O 3 composite oxides with similar specific surface area and adjustable alkalinity. Here, MgO-Al _ 2 O _ 3 composite oxides (Mg/Al atomic ratios are 1/1, 3/1 and 4/1, respectively) are prepared by synthesizing Mg-Al hydrotalcite precursors with uniform structure [19]. For comparison, pure MgO and Al 2 O 3 carriers were also prepared by the same method.

As shown in Table 1, Al _ 2 O _ 3 and the above three MgO-Al _ 2 O _ 3 composite oxides have similar specific surface areas (309 ~ 384 m ~ 2/g), while the specific surface area of MgO is only about half of them (163 m ~ 2/g). This indicates that Al 2 O 3 component in MgO-Al 2 O 3 composite oxide plays a role in supporting the structure of composite oxide and dispersing MgO.

On the other hand, according to the results of CO _ 2 temperature programmed desorption experiment, there are no obvious alkaline sites with medium strength on the surface of Al _ 2 O _ 3, but with the increase of Mg/Al ratio in MgO-Al _ 2 O _ 3 composite oxide, the density of alkaline sites on the surface of the carrier gradually increases. When the carrier is pure MgO, the basic site density of the carrier surface reaches the peak (5. 8 µmol/m 2 )。

The variation of the basic site density of the carrier with the ratio of Mg/Al in the carrier shows that the basic site of MgO-Al 2 O 3 composite oxide mainly comes from the contribution of MgO component, that is, O 2－-bonded with Mg 2＋+has the properties of Lewis base [20]. Especially, Di Cosimo et al. found that introducing a proper amount of Cu into the surface of MgO-Al 2 O 3 composite oxide did not affect the basic sites on the oxide surface [21]. Therefore, Cu/MgO-Al 2 O 3 catalyst and its support have similar basic site density, which is helpful to quantitatively control the basic site density of Cu/MgO-Al 2 O 3 catalyst.